For the period of the nineteenth century, with photography beginning to come on the scene, all photographic images are printed by contact printing. Cameras for that time make “negatives” on coated glass plates or paper. This negative is then placed on top of a paper coated with a light-sensitive emulsion and Contact Printed using sunlight. The resulting positive print will be the exact size of the original negative.
During the early years of photographic history, the only light source available for contact printing is the sun. Since the sun is such an intense light source, use of such a high intensity light requires these early processes to be slow reacting or take a relatively long exposure time to render a positive image with a full tonal scale. There are literally hundreds of different processes invented for hand coating papers that meet these requirements.
Just a few processes for this purpose are: Platinotype (using Platinum), Palladiotype (using Palladium metal to render image), Kallitype, Gum Bichromate, Salt Prints, Cyanotype, and the like. These processes produce very beautiful prints that, for the most part, were of a single color or monochromatic. Most people are familiar with the sepia tone of the old platinum/palladium prints or the bright blue color of the Cyanotype print.
Toward the end of the 19th century and during the first part of the 20th century, some companies even produce machine coated paper that can be purchased and used for a few of these processes. Platinum paper, for example, is available for many years, until wartime shortages occur. The heavy demand for platinum by the arms industry, during World War I for example, causes a dramatic rise in the cost of platinum and makes the process too expensive for the average commercial photographer.
Since these old processes vary greatly in their sensitivity to light, especially light in the ultraviolet range of the spectrum, photographers shorten or lengthen their camera exposures to get a less dense or more dense negative that will in turn do a contact print properly with a given process. This provides their method of contrast control. In addition, methods of altering the chemistry of the paper coatings are discovered which also allow for contrast control, so that the process can be adjusted to the density of the negative.
For the early 20th Century, machine made gelatin silver paper (commonly known as the black and white print) is readily available. Later, gelatin silver paper is used, because it can be developed and printed much faster. In this fashion, this paper may be printed by projecting a small negative onto a large piece of gelatin silver paper with an electric light and some lenses. Such structure provides the darkroom enlarger.
Commercial gelatin silver printing replaces all the old processes because it is cheaper and faster. Gelatin silver printing is preferred, since it can be printed with an enlarger and has the added benefit that smaller cameras with smaller negatives can be used.
The computer age provides the digital camera and the scanner, which cooperate with a computer run by photo processing software. Such software is available under the trademark Photoshop. Such software is used to further refine the digital image file and then print it with an inkjet printer on various papers or send the file to a custom lab with a high end laser or LED imaging device to be imaged on color photographic paper.
The old photographic processes regain popularity, because of their beauty and archival quality. Platinum prints are thought to last 1,000 years without fading. There is a resurgence of interest in using many of the old processes, primarily in the field of fine art photography.
With the advent of the computer and digital imaging, the possibility arises for making enlarged negatives with inkjet printers, image setters, and laser or LED imaging devices-negatives that can be contact printed with all the old processes; and even the modern black and white, gelatin silver papers. To print a negative with an inkjet printer, the inverted image is printed on clear film instead of paper. This negative can then be contact printed on paper sensitized with one of the old process's chemicals.
The problem with current digital negatives revolves around printing a negative properly. In order for a negative to print properly, the density range of the negative must match the density range requirements of the process chemicals used to coat the paper to make the final print. For example, the Gum Bichromate process requires a negative of a shorter density range (Log 0 to log 1.0) than Platinum/Palladium printing (Log 0 to log 1.2 or log 2.5).
There are few ways to adjust this density other than some printer settings and even that is not very accurate and rarely provides the desired density range. So, common practice is to use what is called a Curve Function in Photoshop or another image editing program to change all the image densities to match the density requirements of the process.
The problem with adjusting the density range of the image this way with the Curve Function is that the alteration is so drastic that it compresses and stretches the image densities-resulting in the loss of many of the tonal values in the image. So the final print does not show the rich, full range tonal range that one gets with a traditional in camera negative.